More stringent fuel economy and emissions standards are driving a need for improving the efficiency of both engines and exhaust aftertreatment (AT) systems. One technology that addresses efficiency in engines and AT system is variable valve actuation (VVA). A VVA system can improve AT thermal management, thereby increasing the AT system's efficiency over a duty cycle. A VVA system can also manage pumping losses through turbo/engine work split management (Miller Cycle) or through cylinder deactivation.
Current state-of-the-art VVA systems can be bucketed into two major categories: mechanical and hydraulic. Hydraulic systems have inherently lower efficiency because they sacrifice some/all valve spring energy recovery to achieve VVA functionality. This hydraulic inefficiency increases the engine's brake specific fuel consumption (BSFC) by an estimated 1-3% over a conventional drive cycle. Current mechanical VVA systems have inherently higher efficiencies but also have limited and/or conjoined functionality and limited engine architecture capability; i.e., these systems require overhead cam(s). An improved VVA system would retain the efficiency benefits of a mechanical system but would increase flexibility of use for an array of engine architectures.